When you get to the Yian Garuga level, you must go to area number 7. You must wait until the time limit is expired. You must stay in area number 7 for the entire period. You can do anything in area 7. When time expires, it will say "You have won the battle". You will return to the village, and you must do the mission again. When you find the Garuga, you must fight him. He will die after a few hits.